02 Nov AERATE PONDS AND LAKES: RENEW THEIR LIFE AND OUR PLEASURE
AERATE PONDS AND LAKES: RENEW THEIR LIFE AND OUR PLEASURE
World over the ponds and lakes are destined to die biologically and to disappear to the dislike of vast majority of nature lovers as well as those making a livelihood directly or indirectly out of these. Though the reasons for the degeneration are not unknown, due to other priorities and commitments, scarcely we turn our attention to these water bodies.
However, due to reasons like scarcity of water due to rising demands and impending climate change phenomenon, this natural water harvesting structure began to attract the attention of the society and societal leaders. Yet, at least in our country especially in the semi-arid zones in our country, it seems to me that proposal regarding the clarification of these ponds has restricted itself to utilization of NREGS funds, to cut and remove manually the humus laden mud from the bed of the ponds, if and when these go dry at least partially.
But given the climate of Kerala, the chances for these ponds going dry to allow complete or even partial removal of the accumulated sediment (mud) at the bottom are relatively rare. More over complete desilting of the pond bed goes contrary to the assumption of resulting higher efficiency is also grossly misplaced hydro-geologically.
By desilting process we effectively remove a seamless water seal covering the pond bed. For at least a short period of say 5 to 10 yr., the pond will be a water loosing structure after desilting. Of course there is the plus point of the pond recharging the aquifer. Unfortunately this recharge process sets in as early as the beginning of the rainy season and hence the final aim of recharging the aquifer is also missed.
In other words the aquifer will earn the water leaking from the pond bed and in turn will release it to the streams. Or else, the intent of improving or enhancing the duration of base flow will not materialize at least for a period of under a decade. It is the fine mud that seals the bottom of the pond and restricts the speedy loss to the aquifer.
Menace of Eutrophication
Incidentally, whether they be temple/public/private ponds, due to continued neglect the waters in these structures have reached the peak of eutrophication, which is result of accumulation of nutrients mainly from phosphate based bath or washing soaps, and fertilizer residues or farm discharge. Express symbol of the eutrophication is the luxurious growth of amphibious (both floating and rooted ones along the shores) vegetation, after whose death needs large quantities of oxygen/air for their decay.
Oxygen enters the water only along the water-air interface. As a consequence, eutrophication enhances the organic sedimentation in the pond/lake and attains a peak by encouraging the encroachment by the rooted amphibious plants to the dismay of the users and reduced biodiversity of fish life. When the oxygen level in waters diminishes only very small fish that can survive with little oxygen live in the pond and that too very close to the surface to harvest the little oxygen entering the waters from the air above it. Of course the larger fish cannot survive in these waters, because of the lack or reduced oxygen levels in the bottom layers of the water column.
Status of Ponds in Kerala
This concept though had been in vogue for a long time in t he western societies, had never had a chance to be considered around here in our country, primarily because of our limitations regarding the affordability and partly due to unfamiliarity or exposure. The Kerala Fisheries Development Corporation had published a multi volume set of books called Panfish and in one of those there is a list of districts of Kerala printed against the number of ponds and the aerial coverage.
Anyone who had walked along the embankment along side a pond would know for sure the degree of negligence; these heritage water harvesting structures are in. More over what is also unknown to the non-specialist is the fact that these ponds are destined to be filled over by sediment and organic debris generated in situ as well as these days dumped by the town and city cleaning staff, if periodic revival is not undertaken.
In fact with little more scientific attitude and a desire to salvage these structures, we as a society can conserve the scarce water now and by 2050 with the playing out of the consequences of climate change. Well, again with a changing climate, I very much doubt about the continuation of the pattern of precipitation that we currently receive around here in our state.
In terms of science, all the ponds or at least the majority of ephemeral ponds are in some state of eutrophication. In lay citizens parlance it is the infestation of water surface with floating and fixed or rooted weeds closer to the shoreline in the limewaters. This is the plain consequence of rising levels of nutrients in the pond waters, i.e., due to accumulation of fertilizer residues as well as use of phosphate based soap for washing clothes or bathing. With the rise in nutrients, the waters get enriched in weeds turning the pond water unusable. As the life cycle of these weeds are short, they die early and for the decay put great pressure on the oxygen levels of the water. The oxygen depletion is directly proportional to the density of weeds and inversely proportional to the fish life etc. Scientifically speaking if this process continues, the pond will turn to a marsh and become useless in so far as original intent at the time building of the pond. These ponds are in an advanced state of eutrophication.
In the early stages, the water will acquire a greenish colour from a distance and will only look turbid if taken in the cupped palm of hand. The greenishness is the direct result of presence of algae and the first km in the road to eutrophication.
In this background there is a not so old a technology practiced all over the world for us to consider and adopt. This type of clarification of water bodies is by aeration or if really flush with funds, by the process of oxygenation. This technology came into being with the improvements in the waste water collection, disposal and clarification before discharging into natural water bodies like ponds, streams and rivers.
Aeration is a scaled up version of the aerator in the home aquarium. A properly conceived and design of aerator if installed in the pond/s, the onward march to eutrophication can be decelerated and even reversed in the longer run. There are several internationally known outfits undertaking such tasks, with their outposts in the country.
All the waste water and waters in the ponds and lakes that have reached peak eutrophication can be easily rehabilitated with the aeration process. The chief mechanism among the various methods of aeration is erection of fountains in the ponds and lakes (E.g., Lake Geneva, where these fountains are visible right from the windows of airplanes landing in the runway of the Geneva airport).
Though city center fountains have been considered as symbol of affluence and wealth, when built and operated in the dirty waters of community/temple/public ponds and lakes, they serve the hidden purpose of aerating the waters and reviving the water health of such water bodies
When constructed in the pond or lake, it will be a wonderful attraction to passers by the visitors and leisure seekers during the summer months. Indeed it is a pity that even the GCDA had not yet implemented a set of dancing fountains to the upstream of Venduruthy or Thevara bridges away from the ship channel and harbors in the Kayal, and other places in the lagoons coastal land of Kerala.
Equally potentially ideal locations can be located in the Pookottu kayal, Sasthamkotta kayal or Vellayani Kayal. I might even go to the extent of building such fountains in the temple ponds of most crowded temples of the state like the Padmatheertham, Guruvayoor temple pond and so on.
1. The ponds whether they be in public/temple/private ownerships, all have one thing in common, i.e., they are all under a high degree of eutrophication.
2. Eutrophication is a consequence of abundant supply of nutrients from anthopogenic sources especially in respect of the ponds/lake either close to or in the middle of towns and cities. Eutrophication is a state of a pond, where by the dissolved oxygen is at its lowest level or even absent at least at the sediment water interface. As a consequence the diversity of fish life is reduced to minimum and leaving only small fish to survive and that too along the water-air interface.
3. One of the ways of getting rid of the problem of eutrophication is to build systematically placed water fountains. These play a role very much similar to the aeration pumps we buy and maintain in the home aquarium.